Semiconductor device

ABSTRACT

It is an object of the present invention to connect a wiring, an electrode, or the like formed with two incompatible films (an ITO film and an aluminum film) without increasing the cross-sectional area of the wiring and to achieve lower power consumption even when the screen size becomes larger. The present invention provides a two-layer structure including an upper layer and a lower layer having a larger width than the upper layer. A first conductive layer is formed with Ti or Mo, and a second conductive layer is formed with aluminum (pure aluminum) having low electric resistance over the first conductive layer. A part of the lower layer projected from the end section of the upper layer is bonded with ITO.

This application is a continuation of copending application Ser. No.15/007,916 filed on Jan. 27, 2016 which is a continuation of applicationSer. No. 14/336,333 filed on Jul. 21, 2014 (now U.S. Pat. No. 9,252,227issued Feb. 2, 2016) which is a continuation of application Ser. No.13/967,645 filed on Aug. 15, 2013 (now U.S. Pat. No. 8,786,794 issuedJul. 22, 2014) which is a continuation of application Ser. No.12/978,844 filed on Dec. 27, 2010 (now U.S. Pat. No. 8,514,341 issuedAug. 20, 2013) which is a continuation of application Ser. No.10/576,177 filed on Apr. 19, 2006 (now U.S. Pat. No. 7,859,606 issuedDec. 28, 2010) which is the US national stage of PCT/JP2005/017223 filedon Sep. 13, 2005, all of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a semiconductor device having a circuitwhich includes a thin film transistor (hereinafter referred to as a TFT)and also relates to a manufacturing method thereof. For example, thepresent invention relates to an electronic appliance in which alight-emitting display device having an organic light-emitting elementor an electronic optical device typified by a liquid crystal displaypanel is mounted as its component.

It is to be noted that the semiconductor devices in this specificationindicate all the devices which can operate by using semiconductorcharacteristics, and an electronic optical device, a semiconductorcircuit, and an electronic appliance are all included in thesemiconductor devices.

BACKGROUND ART

In recent years, a technique for forming a thin film transistor (TFT)using a semiconductor thin film (having a thickness of approximatelyseveral nm to several hundred nm) formed over a substrate having aninsulating surface is attracting attention. Thin film transistors arewidely applied to electronic devices such as an IC or an electronicoptical device. In particular, the development of a thin film transistoras a switching element in an image display device is advanced rapidly.

Conventionally, in an active matrix liquid crystal display device drivenby TFTs, a large number of scanning lines and data lines are providedvertically and horizontally over a substrate and a large number of TFTsare provided in accordance with the intersections of these wirings. Ineach TFT, a gate wiring is electrically connected to the scanning line,a source electrode is electrically connected to the data line, and adrain electrode is electrically connected to a pixel electrode.

In a transmissive liquid crystal display device, ITO which has bothlight-transmitting properties and electric conductivity is commonly usedfor the pixel electrode. This pixel electrode and metal wirings such asa data line and a scanning line are insulated by a layer made of aninsulating material. The pixel electrode and the metal wirings are incontact with each other through a contact hole formed at a particularlocation in the insulating film.

As the area of a display screen becomes larger, the delay of a signaldue to the resistance of wirings becomes a more notable problem.Therefore, it is necessary to drastically change the shape of a wiringand an electrode or to use a low-resistant material such as aluminum forthe wiring and the electrode.

When aluminum used as the material of the wiring and the electrodecontacts ITO used as the material of the pixel electrode, a reactioncalled electric erosion occurs at the junction interface. Further, whenaluminum contacts ITO, the surface of aluminum is oxidized and becomeselectrically non-conductive.

Consequently, in order to prevent the electric erosion when the wiring,the electrode, and the like formed with such two incompatible films areconnected, a technique has been suggested in which a metal film having ahigh melting point (such as a titanium film), a metal compound filmhaving a high melting point (such as a titanium nitride film), or thelike is provided between ITO and an aluminum wiring (or electrode) toavoid the electric erosion with ITO.

The present applicant describes in Patent Documents 1 to 3 that a drainof a thin film transistor and ITO serving as a pixel electrode areconnected by sandwiching therebetween a multilayer film including atitanium film, an aluminum film, and a titanium film.

Further, the present applicants describe in Patent Document 4 that adrain of a thin film transistor and ITO serving as a pixel electrode areconnected by sandwiching therebetween a multilayer film including atitanium film and an aluminum film. Moreover, the present applicantsdescribe in Patent Document 5 that a drain of a thin film transistor andITO serving as a pixel electrode are connected by sandwichingtherebetween a multilayer film including a titanium nitride film and analuminum film.

The present applicant also describes in Patent Document 6 that a gateelectrode of a thin film transistor is formed with two layers havingdifferent widths so as to form a GOLD structure.

[Patent Document 1]

Japanese Published Patent Application Laid-Open No.: H9-45927

[Patent Document 2]

Japanese Published Patent Application Laid-Open No.: H10-32202

[Patent Document 3]

Japanese Published Patent Application Laid-Open No.: H6-232129

[Patent Document 4]

Japanese Published Patent Application Laid-Open No.: 2004-6974

[Patent Document 5]

Japanese Published Patent Application Laid-Open No.: H8-330600

[Patent Document 6]

Japanese Published Patent Application Laid-Open No.: 2001-281704

DISCLOSURE OF INVENTION

However, when a titanium film or a titanium nitride film is stackedbetween an aluminum wiring (or electrode) and ITO, the wiring resistanceincreases, which causes an increase in power consumption particularlywhen the display screen has a larger size. The wiring resistance can bedecreased by increasing the cross-sectional area of a metal film to bethe wiring; however, a step difference appears between the surface ofthe substrate and the surface of the thick wiring in the case ofincreasing the cross-sectional area by increasing the film thickness,which causes liquid crystal to have an orientation defect.

Even in an active matrix light-emitting device driven by TFTs, atransparent conductive film may be employed as an anode (or a cathode)of a light-emitting element. Similarly, the anode including thetransparent conductive film is formed over an interlayer insulating filmfor being electrically isolated from various wirings. Therefore, whenITO used as the anode is connected to the electrode (aluminum) of theTFT, the above-mentioned electric erosion occurs in the same way.

It is an object of the present invention to connect a wiring, anelectrode, and the like formed with two incompatible films (an ITO filmand an aluminum film), without increasing the cross-sectional area ofthe wiring, and achieve low power consumption even when a display screenis large.

In the case of manufacturing TFTs by using aluminum as a wiringmaterial, a projection such as a hillock or a whisker may be formed oran aluminum atom may diffuse to a channel-forming region due to heattreatment, thereby causing an operation defect of the TFTs and thedecrease in the characteristics of the TFTs. Consequently, an aluminumalloy film in which another element (for example Si) is contained inaluminum is conventionally used to prevent the generation of the hillockand the like. However, even such an aluminum alloy film cannot solve theproblem in that the junction resistance changes due to the oxidation ofthe aluminum and the reduction of the ITO film at the junctioninterface.

In addition, it is an object of the present invention to prevent thediffusion of an aluminum atom into a channel-forming region even whenaluminum is used as the wiring material and allow good ohmic junction inan active matrix display device.

According to the present invention, an electrode (or a wiring) is formedwith a two-layer structure including a first conductive layer as a lowerlayer and a second conductive layer as an upper layer. The firstconductive layer is formed with metal having a high melting point (suchas Ti or Mo) or metal nitride having a high melting point (such as TiN),and the second conductive layer is formed with aluminum or alloycontaining aluminum. The electrode (or the wiring) having the two-layerstructure has a cross-sectional shape in which the width (W1) of thefirst conductive layer is larger than the width (W2) of the secondconductive layer. In other words, after forming a structure in which anend portion of the lower layer (the first conductive layer) is outerthan an end portion of the upper layer (the second conductive layer), atransparent conductive film is formed so as to cover and contact theelectrode (or the wiring) having the two-layer structure.

According to the present invention, the above problems are solved byconnecting a transparent conductive film (typically ITO) with a part ofthe first conductive layer that is exposed without overlapping thesecond conductive layer in the electrode (or the wiring) including thetwo layers.

According to an aspect of the present invention, a semiconductor devicewhose example is shown in FIG. 1A or 2A comprises a transparentconductive film and a plurality of thin film transistors having asemiconductor thin film over a substrate having an insulating surface,wherein the semiconductor device further comprises an electrode or awiring in which a first conductive layer in contact with thesemiconductor thin film and a second conductive layer on the firstconductive layer are stacked, wherein the first conductive layer has alarger width (W1 or W3) than the second conductive layer, wherein thetransparent conductive film is in contact with a part of the firstconductive layer that extends from an end portion of the secondconductive layer.

According to another aspect of the present invention, a semiconductordevice comprises a transparent conductive film and a plurality of thinfilm transistors having a semiconductor thin film over a substratehaving an insulating surface, wherein the semiconductor device furthercomprises an electrode or a wiring in which a first conductive layer incontact with the semiconductor thin film and a second conductive layeron the first conductive layer are stacked, and wherein the transparentconductive film is in contact with a part of the first conductive layerthat is projected from an end portion of the second conductive layer.

According to another aspect of the present invention, a semiconductordevice comprises a transparent conductive film and a plurality of thinfilm transistors having a semiconductor thin film over a substratehaving an insulating surface, wherein the semiconductor device furthercomprises an electrode or a wiring in which a first conductive layer incontact with the semiconductor thin film and a second conductive layeron the first conductive layer are stacked, wherein a side surfaceportion of the first conductive layer has a smaller tapered angle than aside surface portion of the second conductive film as shown in FIG. 1A,and wherein the transparent conductive film is in contact with the sidesurface portion of the first conductive layer.

According to another aspect of the present invention, a semiconductordevice comprises, as shown in FIG. 3, a transparent conductive film anda plurality of thin film transistors having a semiconductor thin filmover a substrate having an insulating surface, wherein the semiconductordevice further comprises an electrode or a wiring in which a firstconductive layer in contact with the semiconductor thin film and asecond conductive layer on the first conductive layer are stacked, and aflattening insulating film formed over a part of the electrode or thewiring, wherein the transparent conductive film is formed over theflattening insulating film, wherein the electrode or the wiring is incontact with the transparent conductive film through a contact holeprovided in the flattening insulating film, and wherein an end portionof the electrode or the wiring is located in the contact hole.

In each of the above structures, a surface of the second conductivelayer is covered with an oxide film.

Further, a manufacturing method for achieving the above structures isalso included in the present invention. According to a method shownbelow in which etching is conducted multiple times, a structure in whichan end portion of the lower layer (the first conductive layer) is outerthan an end portion of the upper layer (the second conductive layer) isachieved.

As a first method, after forming a mask over a metal multilayer filmincluding two layers, a metal multilayer film pattern having a width W1and a tapered end portion is formed by a first dry etching process.Subsequently, only the upper layer (a material containing aluminum) isanisotropically etched by a second dry etching process to narrow thewidth of the upper layer, thereby forming a width W2 which is smallerthan W1 of the lower layer. As a result, an electrode (or a wiring)where a part of the lower layer not overlapping the upper layer isexposed is formed.

As a second method, after forming a mask over a metal multilayer filmincluding two layers, only the upper layer (a material containingaluminum) is removed by etchant in accordance with the mask pattern. Inthis step, the end portion of the upper layer recedes from the endportion of the mask due to the wraparound of the etching. After that,only a part of the lower layer not covered with the mask is removed by adry etching process. As a result, an electrode (or a wiring) where apart of the lower layer not overlapping the upper layer is exposed isformed.

As a third method, after forming a mask over a metal multilayer filmincluding two layers, a metal multilayer film pattern is formed by a dryetching process. Subsequently, only the upper layer (a materialcontaining aluminum) is processed by etchant, thereby narrowing thewidth of the upper layer. In this step, the end portion of the upperlayer recedes from the end portion of the mask due to the wraparound ofthe etching. As a result, an electrode (or a wiring) where a part of thelower layer not overlapping the upper layer is exposed is formed.

As a fourth method, after forming a first mask over a metal multilayerfilm including two layers, a metal multilayer film pattern is formed bya dry etching process or a wet etching process. Subsequently, afterremoving the first mask, a second mask is formed, and the metalmultilayer film pattern is processed in accordance with the second maskpattern. In this step, the second mask pattern is made narrower than thefirst mask pattern. As a result, an electrode (or a wiring) where a partof the lower layer not overlapping the upper layer is exposed is formed.

In any one of the above methods, the electrode or the wiring ispatterned by using a photomask through dry etching using a plasmaapparatus or wet etching using etchant.

Then, a transparent conductive film is formed so as to cover and contactthe electrode (or the wiring) obtained by the above method. As a result,the lower layer of the electrode (or the wiring) and the transparentconductive film are in contact with each other so that they areelectrically connected to each other in this portion principally.

A structure in which the transparent conductive film and the lower layerare in contact at the end section of the lower layer has already beendisclosed conventionally; however, in most of conventional structures,the transparent conductive film mainly contacts the top surface of theuppermost layer so that they are electrically connected to each other.Meanwhile, in the present invention, in order to electrically connectthe lower layer and the transparent conductive film, a tapered portionhaving a smaller tapered angle than the upper layer or a portionprojected from the end section of the upper layer is intentionallyprovided to secure the area where the lower layer and the transparentconductive film contact, so that the lower layer and the transparentconductive film completely contact with each other.

According to the present invention, since a thin oxide film is formedbetween the transparent conductive film and the upper layer formed witha material containing aluminum, the upper layer and the transparentconductive film are not directly connected, and they are electricallyconnected through the lower layer interposed therebetween. The structureof the present invention is greatly different in this point fromconventional structures.

It is to be noted that a light-emitting element has an anode, a cathode,and a layer containing an organic compound which provides luminescence(Electro Luminescence) by applying an electric field thereto (this layeris hereinafter referred to as an EL layer). Luminescence from theorganic compound includes light emitted when a singlet-excited statereturns to a ground state (fluorescence) and light emitted when atriplet-excited state returns to the ground state (phosphorescence). Ina light-emitting device manufactured by a film-forming apparatus and afilm-forming method according to the present invention, eitherfluorescence or phosphorescence can be used.

Further, in this specification, a first electrode indicates an electrodeserving as an anode or a cathode of the light-emitting element. Thelight-emitting element has a structure including the first electrode, alayer containing an organic compound over the first electrode, and asecond electrode over the layer containing the organic compound. Theelectrode formed over a substrate first is referred to as the firstelectrode.

As arrangement of the first electrode, stripe arrangement, deltaarrangement, mosaic arrangement, or the like can be used.

The light-emitting device in this specification indicates an imagedisplay device, a light-emitting device, or a light source (including anillumination device). Moreover, a module in which a connector, forexample an FPC (Flexible Printed Circuit), a TAB (Tape AutomatedBonding) tape, or a TCP (Tape Carrier Package) is attached to alight-emitting device, a module in which a printed wiring board isprovided at a tip of a TAB tape or a TCP, and a module in which an IC(Integrated Circuit) is directly mounted in a light-emitting element bya COG (Chip On Glass) method are all included in the light-emittingdevice.

In the light-emitting device according to the present invention, thedriving method of screen displaying is not particularly limited. Forexample, a point sequential driving method, a line sequential drivingmethod, a plane sequential driving method, or the like may be used.Typically, the line sequential driving method is used, and a timedivision gradation driving method or an area division gradation drivingmethod may be appropriately used. Further, a video signal to be inputtedinto a source line of the light-emitting device may be either an analogsignal or a digital signal. A driver circuit and the like may bedesigned appropriately in accordance with the video signal.

In a light-emitting device in which a video signal is digital, the videosignal to be inputted into a pixel may use constant voltage (CV) orconstant current (CC). When the video signal uses the constant voltage(CV), the voltage applied to the light-emitting element is constant(CVCV) or the current flowing through the light-emitting element isconstant (CVCC). On the other hand, when the video signal uses theconstant current (CC), the voltage applied to the light-emitting elementis constant (CCCV) or the current flowing in the light-emitting elementis constant (CCCC).

In the light-emitting display device according to the present invention,a protective circuit (such as a protective diode) may be provided toavoid electrostatic damage.

In the case of an active matrix type, a plurality of TFTs are providedso as to connect with the first electrode, and the present invention canbe applied regardless of the TFT structure. For example, a top-gate TFT,a bottom-gate (inverted staggered) TFT, or a staggered TFT can be used.Not only a TFT of a single-gate structure but also a multi-gate TFThaving a plurality of channel-forming regions, for example a double-gateTFT, may be used.

A TFT to be electrically connected with the light-emitting element maybe either a p-channel TFT or an n-channel TFT. When the light-emittingelement is connected with the p-channel TFT, the light-emitting elementis connected with the anode. Concretely, after stacking a hole-injectinglayer/a hole-transporting layer/a light-emitting layer/anelectron-transporting layer sequentially over the anode, the cathode maybe formed. When the light-emitting element is connected with then-channel TFT, the light-emitting element is connected with the cathode.Concretely, after stacking an electron-transporting layer/alight-emitting layer/a hole-transporting layer/a hole-injecting layersequentially over the cathode, the anode may be formed.

As a channel-forming region of the TFT, an amorphous semiconductor film,a semiconductor film including a crystal structure, a compoundsemiconductor film including an amorphous structure, or the like can beappropriately used. Further, as a channel-forming region of the TFT, asemi-amorphous semiconductor film (also referred to as a microcrystalsemiconductor film) can also be used. The semi-amorphous semiconductorfilm has an intermediate structure between an amorphous structure and acrystal structure (including a single crystal and polycrystal) and has athird state which is stable in terms of free energy. The semi-amorphoussemiconductor film also includes a crystalline region which has ashort-range order and a lattice distortion.

In this specification, the pixel electrode indicates an electrode to beconnected with a TFT and also indicates an electrode paired with anopposing electrode provided to an opposing substrate. Further, a liquidcrystal element indicates the pixel electrode, the opposing electrode,and a liquid crystal layer provided between these electrodes. In anactive matrix liquid crystal display device, a display pattern is formedon the screen by driving the pixel electrodes arranged in matrix.Specifically, the liquid crystal layer provided between the pixelelectrode and the opposing electrode is optically modulated by applyingvoltage between the selected pixel electrode and the opposing electrodecorresponding to the pixel electrode, and this optical modulation isrecognized as a display pattern by an observer.

According to the present invention, the step of providing a layercontaining metal having a high melting point as the upper layer of thewiring which has been conventionally required can be omitted withoutincreasing the contact resistance between the electrode (or the wiring)and the pixel electrode. This provides advantages in that cost and timespent in the production can be reduced.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B are cross-sectional views of a pixel showing EmbodimentMode 1;

FIGS. 2A and 2B are cross-sectional views of a pixel showing EmbodimentMode 2;

FIG. 3 is a cross-sectional view of a pixel showing Embodiment Mode 3;

FIGS. 4A and 4B are SEM photographs and FIG. 4C is a perspective view,all of which show an end portion of an etched electrode;

FIGS. 5A and 5B show a first TEG pattern;

FIGS. 6A and 6B show a second TEG pattern;

FIG. 7 is a graph showing a result of electric measurement using thefirst TEG pattern (an experiment result of multilayer including titaniumand aluminum);

FIG. 8 is a graph showing a result of electric measurement using thesecond TEG pattern;

FIG. 9 is a cross-sectional view of an EL display panel (Embodiment 1);

FIG. 10 is a cross-sectional view of an EL display panel (Embodiment 2);

FIGS. 11A and 11B are top views showing an EL display panel (Embodiment3);

FIG. 12 is a cross-sectional view showing a liquid crystal panel(Embodiment 4);

FIGS. 13A to 13H show examples of electronic appliances;

FIG. 14 shows an example of an electronic appliance; and

FIG. 15 is a graph showing a result of electric measurement using thefirst TEG pattern (an experiment result of multilayer includingmolybdenum and aluminum).

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment Modes of the present invention are hereinafter described.

Embodiment Mode 1

The present invention is described using an active matrix light-emittingdevice as an example in this embodiment mode.

FIG. 1A is a magnified cross-sectional view showing a part of a pixelportion of a light-emitting device. Steps of manufacturing asemiconductor device having a light-emitting element shown in FIG. 1Aare shown below.

First, a base insulating film 11 is formed over a substrate 10. In thecase of extracting light assuming that the side of the substrate 10 is adisplay surface, a glass substrate or a quartz substrate havinglight-transmitting properties is preferably used as the substrate 10.Moreover, a plastic substrate which has light-transmitting propertiesand which can resist the process temperature may be used. Meanwhile, inthe case of extracting light assuming that a plane opposite to the sideof the substrate 10 is a display surface, a silicon substrate, a metalsubstrate, or a stainless steel substrate each having an insulating filmformed thereover may be used besides the above-mentioned substrates.Here, a glass substrate is used as the substrate 10. It is to be notedthat the glass substrate has a refractive index of approximately 1.55.

As the base insulating film 11, a base film including an insulating filmsuch as a silicon oxide film, a silicon nitride film, or a siliconoxynitride film is formed. Although an example of using a two-layerstructure is shown as the base film here, the base film may have asingle-layer structure or a multilayer structure in which two or morelayers are stacked. It is to be noted that the base insulating film isnot necessarily formed.

Subsequently, a semiconductor layer is formed over the base insulatingfilm. The semiconductor layer is formed in such a way that after forminga semiconductor film having an amorphous structure by a known means (asputtering method, an LPCVD method, a plasma CVD method, or the like),the semiconductor film is crystallized so as to be a crystallinesemiconductor film by a known crystallization process (a lasercrystallization method, a thermal crystallization method, a thermalcrystallization method using a catalyst such as nickel, or the like),and then the crystalline semiconductor film is patterned into a desiredshape using a first photomask. The thickness of the semiconductor layeris set in the range of 25 to 80 nm (preferably 30 to 70 nm). Althoughthe material of the crystalline semiconductor film is not limited inparticular, it is preferable to use silicon or silicon germanium (SiGe)alloy.

In the crystallization process of the semiconductor film having theamorphous structure, a continuous wave laser may be used. In order toobtain a crystal having a large grain size by crystallizing theamorphous semiconductor film, it is preferable to use any one of secondto fourth harmonics of a fundamental wave emitted from a continuous wavesolid-state laser. Typically, the second harmonics (532 nm) or the thirdharmonics (355 nm) of a Nd:YVO₄ laser (fundamental wave 1064 nm) ispreferably used. In the case of using the continuous wave laser, a laserbeam emitted from a continuous wave YVO₄ laser is driven by 10 W isconverted into a harmonics by a non-linear optical element. Theharmonics can also be obtained by putting a YVO₄ crystal and anon-linear optical element in the resonator. It is preferable to shapethe laser beam into a rectangular or elliptical laser beam on anirradiation surface by an optical system and then deliver the laser beamto an object. The energy density here is required to be in the range ofapproximately 0.01 to 100 MW/cm² (preferably 0.1 to 10 MW/cm²). Then,the semiconductor film is preferably moved at a speed of approximately10 to 2000 cm/s relative to the laser beam.

Next, after removing the resist mask, a gate insulating film 12 isformed so as to cover the semiconductor layer. The gate insulating film12 is formed in thicknesses from 1 to 200 nm by a plasma CVD method or asputtering method.

Next, a conductive film having thicknesses from 100 to 600 nm is formedover the gate insulating film 12. Here, a conductive film is formed withmultilayer including a TaN film and a W film by a sputtering method.Although the conductive film is formed with the multilayer including theTaN film and the W film here, the structure is not limited inparticular. A single layer or multilayer containing an element selectedfrom Ta, W, Ti, Mo, Al, and Cu or an alloy material or a compoundmaterial containing the above element as its main component may beformed. Alternatively, a semiconductor film typified by apoly-crystalline silicon film doped with an impurity element such asphosphorus may be used.

Next, a resist mask is formed using a second photomask. Etching isconducted by a dry etching method or a wet etching method. Through thisetching step, the conductive film is etched, thereby obtainingconductive layers 14 a and 14 b. These conductive layers 14 a and 14 bserve as a gate electrode of a TFT.

Next, after removing the resist mask, a resist mask is newly formedusing a third photomask. A first doping step is conducted to dope thesemiconductor with an impurity element imparting n-type conductivity(typically, phosphorus or arsenic) at low concentration so that ann-channel TFT (not shown) is formed. The resist mask covers a region tobe a p-channel TFT and a vicinity of the conductive layer. The firstdoping step is conducted through an insulating film, thereby forming alow-concentration impurity region. One light-emitting element is drivenby a plurality of TFTs, and when only p-channel TFTs are used to drive,the above doping step is not necessary in particular.

Subsequently, after removing the resist mask, a resist mask is newlyformed using fourth photomask. A second doping step is conducted inorder to dope the semiconductor with an impurity element impartingp-type conductivity (typically boron) at high concentration. The seconddoping step is conducted through the gate insulating film 12, therebyforming p-type high-concentration impurity regions 17 and 18.

Next, a resist mask is newly formed using a fifth mask. A third dopingstep is conducted to dope the semiconductor with an impurity elementimparting n-type conductivity (typically, phosphorus or arsenic) at highconcentration so that an n-channel TFT (not shown) is formed. The thirddoping step is conducted by an ion doping method under a condition wherethe dose ranges from 1×10¹³ to 5×10¹⁵/cm² and the accelerating voltageranges from 60 to 100 keV. The resist mask covers a region to be ap-channel TFT and a vicinity of the conductive layer. The third dopingstep is conducted through the gate insulating film 12, thereby formingn-type high-concentration impurity regions.

After that, the resist mask is removed and then a first interlayerinsulating film 13 containing hydrogen is formed. Subsequently,activation of the impurity element added in the semiconductor layer andhydrogenation are conducted. As the first interlayer insulating film 13containing hydrogen, a silicon nitride oxide film (SiNO film) obtainedby a PCVD method is used. In addition, when a metal element for inducingcrystallization, typically nickel, is used to crystallize thesemiconductor film, gettering to reduce nickel in a channel-formingregion 19 can be conducted at the same time as the activation.

Next, a flattening insulating film 16 to be a second interlayerinsulating film is formed. As the flattening insulating film 16, aninsulating film whose skeletal structure includes a bond of silicon (Si)and oxygen (O) obtained by a coating method is used.

Next, etching is conducted using a sixth mask to form a contact hole inthe flattening insulating film 16. At the same time, a part of theflattening insulating film at a periphery of the substrate is removed.Here, the etching is conducted under a condition where the selectiveratio between the first interlayer insulating film 13 and the flatteninginsulating film 16 is different. Although the etching gas to be used isnot limited, CF₄, O₂, He, and Ar are appropriate. The dry etching isconducted under a condition where the RF power is 3000 W, the pressureis 25 Pa, and the flow rates of CF₄, O₂, He, and Ar are 380 sccm, 290sccm, 500 sccm, and 500 sccm respectively. In order to etch so as not toleave residue on the first interlayer insulating film 13, the etchingtime is preferably increased for approximately 10 to 20%. The flatteninginsulating film 16 may be tapered by conducting etching once or multipletimes. Here, the dry etching is conducted twice, and the second dryetching is conducted under a condition where the RF power is 3000 W, thepressure is 25 Pa, and the flow rates of CF₄, O₂, and He are 550 sccm,450 sccm, and 350 sccm respectively. It is desirable that the endportion of the flattening insulating film have a tapered angle θ morethan 30° and less than 75°.

Next, etching is conducted using the sixth mask again, therebyselectively removing the exposed parts of the gate insulating film 12and the first interlayer insulating film 13. Specifically, the gateinsulating film 12 and the first interlayer insulating film 13 areetched using CHF₃ and Ar as etching gas. In order to conduct the etchingso as not to leave residue over the semiconductor layer, the etchingtime is preferably increased for approximately 10 to 20%.

Next, the sixth mask is removed, and then a conductive film having atwo-layer structure which contacts the semiconductor layer in thecontact hole is formed. A first conductive layer 22 a to be a lowerlayer is formed with metal having a high melting point (such as Ti orMo) or a metal compound having a high melting point (such as TiN). Thefilm thickness of the first conductive layer 22 a ranges from 20 to 200nm. The first conductive layer 22 a to be the lower layer has anadvantage of preventing the interactive diffusion of silicon andaluminum.

Further, a second conductive layer 22 b to be an upper layer is formedwith low-resistant metal (typically Al) in order to decrease theelectric resistance of the wiring. The film thickness of the secondconductive layer 22 b ranges from 0.1 to 2 μm. It is preferable to formthese two layers continuously in the same sputtering apparatus so thatthe surface of each layer is not oxidized.

Next, first etching is conducted using a seventh mask. The first etchingis conducted so that the upper layer is patterned to have a width W1.The first etching is conducted by a dry etching method or a wet etchingmethod.

Next, as the resist mask remains, second etching is conducted by an ICP(Inductively Coupled Plasma) etching method to etch the secondconductive layer to have a width W2 while making the resist mask recede.By the second etching, the first conductive layer is also removedslightly, thereby forming a tapered portion. By employing the ICPetching method, the film can be etched into a desired tapered shape whenthe etching condition (the electric power applied to a coil electrode,the electric power applied to an electrode on a substrate side, theelectrode temperature on the substrate side, and so on) is appropriatelyadjusted. As the etching gas, chlorine-based gas typified by Cl₂, BCl₃,SiCl₄, or CCl₄, fluorine-based gas typified by CF₄, SF₆, or NF₃, or O₂can be appropriately used.

Further, when the tapered shape is formed by the ICP etching method,projecting portions are formed equally at opposite sides of theelectrode. Depending on the second etching condition, a part of theflattening insulating film 16 that is exposed by etching the firstconductive layer may also be slightly etched.

Next, a transparent conductive film is formed in contact with theelectrode or the wiring having the above two-layer structure. When thetransparent conductive film and the first conductive layer 22 a areformed so as to be in direct contact with each other, good ohmicjunction can be obtained. Then, etching is conducted using an eighthmask, thereby forming first electrodes 23R and 23G, which are anodes (orcathodes) of organic light-emitting elements.

As the material for the first electrode, ITO (indium tin oxide) or ITSO(indium tin oxide containing silicon oxide obtained by a sputteringmethod using a target of ITO which contains silicon oxide by 2 to 10 wt%) is used. In addition to ITSO, a transparent conductive film such as alight-transmitting conductive oxide film (IZO), which is indium oxidecontaining silicon oxide in which zinc oxide (ZnO) is mixed by 2 to 20%may be used. Further, a transparent conductive film of ATO (antimony tinoxide) containing silicon oxide may be used.

If ITO is used as the first electrodes 23R and 23G, bake forcrystallization is conducted to decrease the electric resistance. ITSOand IZO, even after conducting bake, are not crystallized like ITO andremain to be amorphous.

In order to compare the contact resistance between ITSO and theelectrode of the two layers obtained by the above method and the contactresistance in a comparative example, the following experiment is carriedout.

A silicon oxide film is formed over a glass substrate as an insulatinglayer. Then, a metal layer having a two-layer structure is formed bycontinuously stacking a pure aluminum layer (having a thickness of 700nm and a resistivity of 4 μΩcm) on a titanium layer (of 100 nm thick) bya sputtering method. After that, a resist mask having an electrodepattern is formed by photolithography, and two samples are formed byetching the metal layer having the two-layer structure by the followingthree methods.

In a sample 1 (comparative example), both of the two layers of the metallayer are etched only by conducting plasma etching once with the use ofan ICP apparatus. As a result, an end section of the formed electrodehas a tapered angle of approximately 80° which is almost perpendicular.After that, an ITSO film to be a transparent electrode is formed by asputtering method, and then patterned through photolithography.

In a sample 2 (the present invention), the metal layer having thetwo-layer structure is etched by conducting plasma etching in two stepswith the use of an ICP apparatus, thereby obtaining a shape in which thetitanium layer as the lower layer is projected. Specifically, firstetching is conducted so that the end section of the etched electrode hasa tapered angle of approximately 60° and second etching different fromthe first etching condition is conducted so that the aluminum layer asthe upper layer is selectively etched and the end section becomes almostperpendicular.

The first etching is conducted for 100 seconds under a first conditionwhere BCl₃ and Cl₂ are used as the etching gas, the flow rate of BCl₃and Cl₂ is 60/20 (sccm), the pressure is 1.9 Pa, and an RF (13.56 MHz)electric power of 450 W is applied to the coil-shaped electrode togenerate plasma. An RF (13.56 MHz) electric power of 100 W is alsoapplied to the substrate side (sample stage) to apply substantiallynegative bias voltage. The electrode on the substrate side has an areaof 12.5 cm×12.5 cm and the coil-shaped electrode (here a quartz circularplate on which a coil is provided) is a circular plate having a diameterof 25 cm. Next, the etching is conducted for 160 seconds under a secondcondition where the etching gas and the flow rate are the same as thosein the first condition, the pressure is 1.2 Pa, and an RF electric powerof 600 W is applied to the coil-shaped electrode and an RF electricpower of 250 W is applied to the substrate side to generate plasma.

A condition of the second etching is that BCl₃ and Cl₂ are used as theetching gas with the gas flow rate of 40/40 (sccm), the pressure is 3.5Pa, an RF electric power of 200 W is applied to the coil-shapedelectrode and an RF electric power of 50 W is applied to the substrateside to generate plasma, and the etching time is 60 seconds.

FIGS. 4A and 4B are SEM (scanning electron microscope) photographs afterthe etching, and FIG. 4C is a schematic cross-sectional view. FIG. 4A isa perspective view, and FIG. 4B is a cross-sectional view. The length ofthe projected portion is 0.22 μm. In other words, the end portion of theupper layer and the end portion of the lower layer are 0.22 μm apart,and the width W1 of the lower layer is 0.44 μm larger than the width W2of the upper layer. After that, an ITSO film to be a transparentelectrode is formed by a sputtering method and patterned throughphotolithography.

In each of the two samples, two kinds of TEG (test element group)patterns are formed for electric resistance measurement.

One of the TEG patterns is a first TEG pattern (FIG. 5A shows atop-surface layout, and FIG. 6B shows a relation of measured value inthe magnified contact portion) referred to as a contact chain in whichthe metal layer and the ITSO layer are arranged alternately so as to beserially connected. In the first TEG pattern, three resistance elementsof the wiring, the ITO, and the interface therebetween are seriallyconnected.

The other pattern is a second TEG pattern (FIG. 6A shows a top-surfacelayout and FIG. 6B shows a relation of the measured values in themagnified contact portion) in which the metal layer and the ITSO layercrisscross with each other for Kelvin measurement.

Next, the electric resistance is measured using the first TEG patternson the two samples. As a result, the resistance value (per one contact)at 1 V in the sample 2 (the present invention) is 77% lower than that inthe sample 1 (comparative example).

Further, FIG. 7 shows a result of measuring the electric resistance ofthe first TEG. It is to be noted that the resistivity of ITSO is assumedto be 4000 μΩcm.

Moreover, the electric resistance is measured using the second TEGpatterns on the two samples. The contact resistance value is lower inthe sample 2 (the present invention) than in the sample 1 (comparativeexample). FIG. 8 shows a result of the electric resistance measurementon the second TEG pattern.

It is to be understood from the above experiments that the contactresistance with ITSO can be decreased by using the electrode of thetwo-layer structure in which the lower layer (titanium layer) isprojected.

FIG. 15 shows a result of the electric resistance measurement on thefirst TEG pattern using a molybdenum layer (of 100 nm thick) instead ofthe lower layer (titanium layer). It is to be noted that the resistivityof ITSO is assumed to be 4000 μΩcm. In FIG. 15, a solid line shows acomparative sample which is etched under a condition for making the endsection of the molybdenum layer serving as the lower layer almostvertical. Further, in FIG. 15, the sample in which the molybdenum layerserving as the lower layer is projected and the end section has atapered angle of approximately 60° is illustrated as x marks. It is alsounderstood from FIG. 15 that the contact resistance with ITSO can bedecreased by using the electrode having the two-layer structure in whichthe lower layer (molybdenum layer) is projected.

Moreover, the electric resistance is measured in the same way underdifferent conditions of the thickness of the lower layer: 100 nm, 200nm, and 300 nm. Then, it has been confirmed that the contact resistancevalue gets lower as the lower layer is thicker.

Further, FIG. 1B is a magnified cross-sectional view showing a partwhere the first electrode formed with a transparent conductive film andthe lower layer formed with Ti are in contact. As shown in FIG. 1B, analuminum oxide film 34 is formed thinly on the surface of the secondconductive layer 22 b to be the upper layer, and the first electrodeformed with the transparent conductive film is electrically bonded withonly the lower layer. FIG. 1B shows an example in which a tapered angleα of the end portion of the lower layer 22 a is smaller than a taperedangle β of the end portion of the second conductive layer 22 b to be theupper layer. The area where the first electrode and the first conductivelayer contact increases as the tapered angle α of the end portion of thefirst conductive layer 22 a to be the lower layer is smaller.

Subsequently, an insulator 29 (referred to as a bank, a partition wall,a barrier, an embankment, or the like) is formed to cover the endportions of the first electrodes 23R and 23G using the eighth mask. Asthe insulator 29, an organic resin film obtained by a coating method oran SOG film (such as a SiO_(x) film containing an alkyl group) is formedin thicknesses from 0.8 to 1 μm.

Next, layers 24R and 24G each containing an organic compound are stackedby an evaporation method or a coating method. In addition, it isdesirable to conduct vacuum heating for degassing in order to improvethe reliability before forming the layers 24R and 24G containing theorganic compound. For example, it is desirable to conduct heat treatmentat 200 to 300° C. under a low-pressure atmosphere or an inert atmosphereto remove the gas contained in the substrate before evaporating theorganic compound materials. The layers 24R and 24G containing theorganic compound are formed by an evaporation method in a film-formingchamber which is evacuated so as to have a degree of vacuum at 5×10⁻³Torr (0.665 Pa) or less, preferably in the range of 10⁻⁴ to 10⁻⁶ Torr.At the evaporation, the organic compound is vaporized in advance byresistance heating, and the vaporized organic compound spatters towardthe substrate by opening the shutter. The vaporized organic compoundspatters upward and goes through an opening portion provided to a metalmask, and then is deposited onto the substrate.

In order to achieve a full color, the mask is aligned for each of theemission colors (R, G, and B).

The layers 24R and 24G containing the organic compound are multilayerformed by stacking a hole-injecting layer/a hole-transporting layer/alight-emitting layer/an electron-transporting layer sequentially overthe first electrode. For example, Alq₃ doped with DCM is formed in 40 nmthick as a light-emitting layer in the layer 24R containing the organiccompound. Moreover, Alq₃ doped with DMQD is formed in 40 nm thick as alight-emitting layer in the layer 24G containing the organic compound.Although not illustrated here, PPD(4,4′-bis(N-(9-phenanthryl)-N-phenylamino)biphenyl) doped with CBP(4,4′-bis(N-carbazolyl)-biphenyl) is formed in 30 nm thick as a bluelight-emitting layer, and SAlq(bis(2-methyl-8-quinolinolate)(triphenylsilanolato)aluminum) is formedin 10 nm thick as a blocking layer.

Next, a second electrode 25, that is, a cathode (or an anode) of theorganic light-emitting element is formed. As the material of the secondelectrode 25, alloy such as MgAg, MgIn, or AlLi, CaF₂, CaN, or a filmformed by co-evaporating aluminum and an element belonging to the firstor second group in the periodic table may be used.

Before forming the second electrode 25, a light-transmitting layer maybe formed with CaF₂, MgF₂, or BaF₂ as a cathode buffer layer inthicknesses from 1 to 5 nm.

Moreover, a protective layer for protecting the second electrode 25 maybe formed.

Subsequently, the light-emitting element is sealed by pasting a sealingsubstrate 33 with a sealing material (not shown). Dry inert gas or atransparent filling material fills a region 27 surrounded by a pair ofsubstrates and the sealing material. As the inert gas, noble gas ornitrogen can be used, and a dry agent for drying is provided to the sealsubstrate 33. As the filling material, any material can be used as longas the material has light-transmitting properties. Typically,ultraviolet curable or thermosetting epoxy resin may be used. When thefilling material fills the space between the pair of substrates, thetransmittance of the whole can be increased.

When the first electrode is formed with a transparent material and thesecond electrode is formed with a metal material, a structure in whichlight is extracted through the substrate 10, which is a so-calledbottom-emission type, is obtained. Further, when the first electrode isformed with a metal material and the second electrode is formed with atransparent material, a structure in which light is extracted throughthe sealing substrate 33, which is a so-called top-emission type, isobtained. Furthermore, when the first electrode and the second electrodeare formed with a transparent material, a structure in which light isextracted from both of the substrate 10 and the sealing substrate 33 canbe obtained. The present invention may employ any one of the abovestructures appropriately.

The layers through which light emitted from the light-emitting layerpasses when light is extracted through the substrate 10, which are thefirst electrode, the first interlayer insulating film 13, the secondinterlayer insulating film 16, the gate insulating film 12, and the baseinsulating film 11, all include silicon oxide (refractive indexapproximately 1.46); therefore, the difference of the refractive indexis small, thereby increasing the light extraction efficiency. That is tosay, stray light between the layers formed with the materials havingdifferent refractive indexes can be suppressed.

Embodiment 2

Here, an example in which an electrode having a two-layer structurewhose shape is different from that in Embodiment Mode 1 is hereinafterdescribed with reference to FIGS. 2A and 2B.

Since the steps except the step of forming an electrode including afirst conductive layer 222 a and a second conductive layer 222 b are thesame as those in Embodiment Mode 1, the detailed description is omittedhere. Therefore, in FIGS. 2A and 2B, the same part as that in FIG. 1A isdenoted with the same reference numeral.

A conductive film including a two-layer structure in contact with thesemiconductor layer in the contact hole is formed in accordance withEmbodiment Mode 1. The first conductive layer 222 a to be a lower layeris formed with metal having a high melting point (such as Ti or Mo) or ametal compound having a high melting point (such as TiN) in thicknessesfrom 20 to 200 nm. The first conductive layer 222 a to be the lowerlayer has an advantage of preventing the interactive diffusion ofsilicon and aluminum.

The second conductive layer 222 b to be an upper layer is formed withlow-resistant metal (typically Al) in thicknesses from 0.1 to 2 μm inorder to lower the electric resistance of the wiring. It is preferableto form these two layers continuously in the same sputtering apparatusso that the surface of each layer is not oxidized.

Next, first etching is conducted using the seventh mask. By the firstetching, the upper layer is patterned so as to have a width W4. Thefirst etching is conducted by a dry etching method or a wet etchingmethod.

Next, second etching is conducted using the eighth mask. By the secondetching, the lower layer is patterned so as to have a width W3. Thesecond etching is conducted by a dry etching method or a wet etchingmethod.

At the first and second etching, the width W4 of the upper layer isdetermined by the seventh mask, and the width W3 of the lower layer isdetermined by the eighth mask.

Next, in the same way as Embodiment Mode 1, a transparent conductivefilm is formed in contact with the electrode or the wiring having thetwo-layer structure. When the transparent conductive film and the firstconductive layer 222 a are formed so as to be in direct contact witheach other, good ohmic junction can be obtained. Then, etching isconducted using a ninth mask, thereby forming first electrodes 23R and23G, which are anodes (or cathodes) of organic light-emitting elements.

The following steps are the same as those in Embodiment Mode 1;therefore, the detailed description is omitted here.

Here, the example of obtaining the electrode structure shown in FIG. 2Aby patterning twice to form the projected portion is shown. In the caseof patterning twice, the projected portions can be formed equally at theopposite sides of the upper layer as shown in Embodiment Mode 1 and theprojected portion can also be formed only at the portion that overlapsthe first electrode to be formed afterward. In other words, the size ofthe area where the first electrode and the lower layer contact can becontrolled by appropriately designing the two patterning masks.

FIG. 2B is a magnified cross-sectional view showing a portion where thefirst electrode formed with the transparent conductive film and thelower layer formed with Ti are in contact. As shown in FIG. 2B, analuminum film 34 is thinly formed on the surface of the secondconductive layer 222 b, and the first electrode formed with thetransparent conductive film is electrically bonded with only the lowerlayer. In FIG. 2B, a tapered angle α of the end portion of the firstconductive layer 222 a to be the lower layer is larger than a taperedangle β of the end portion of the second conductive layer 222 b. Asshown in FIG. 2B, the top surface portion and the end section of thelower layer are electrically connected with the first electrode. Thearea where the first electrode is in contact with the end section of thelower layer is larger than the area where the first electrode is incontact with the top surface of the lower layer.

This embodiment mode can be freely combined with Embodiment Mode 1.

Embodiment Mode 3

An example of providing one more insulating film between a transparentconductive film and an electrode having a two-layer structure ishereinafter described with reference to FIG. 3.

Since the steps up to forming an electrode including a first conductivelayer 22 a, a second conductive layer 22 b are the same as those inEmbodiment Mode 1, the detailed description is omitted. Further, in FIG.3, the same part as that in FIG. 1A is denoted with the same referencenumeral.

First, the electrodes 22 a and 22 b having the two-layer structure areformed in accordance with the step shown in Embodiment Mode 1. Next, aflattening insulating film 320 to be a third interlayer insulating filmis formed. As the flattening insulating film 320, an insulating filmwhose skeletal structure includes a bond of silicon (Si) and oxygen (O)obtained by a coating method is used. Here, the third flatteninginsulating film 320 is used for flattening, the flattening insulatingfilm 16 is not necessarily flat, and for example, an inorganicinsulating film formed by a PCVD method may be used.

Next, the flattening insulating film 320 is selectively etched, therebyforming a contact hole that reaches the second conductive layer 22 b tobe the upper layer and the flattening insulating film 16. Subsequently,the transparent conductive film is formed and patterned to form firstelectrodes 323R and 323G.

Next, an insulator 329 covering end portions of the first electrodes323R and 323G is formed in the same way as the step shown in EmbodimentMode 1. Since the following steps are the same as those in EmbodimentMode 1, the detailed description is omitted here.

By having the structure shown in FIG. 3, the area of the first electrodecan be expanded and the light-emitting region can be expanded.

This embodiment mode can be freely combined with Embodiment Mode 1 orEmbodiment Mode 2.

The present invention having the above structure is described in moredetail with reference to Embodiments shown below.

Embodiment 1

This embodiment describes a full-color light-emitting device withreference to FIG. 9 which shows a cross section of a part of an activematrix light-emitting device.

Three TFTs 1003R, 1003G, and 1003B are provided over a first substrate1001 where a base insulating film 1002 is provided. These TFTs arep-channel TFTs each having a channel-forming region 1020, source ordrain regions 1021 and 1022, a gate insulating film 1005, and a gateelectrode. The gate electrode has two layers of a tapered lower layer1023 a of the gate electrode and an upper layer 1023 b of the gateelectrode.

Further, an interlayer insulating film 1006 is an inorganic insulatingfilm. A flattening insulating film 1007 covering the interlayerinsulating film 1006 is a flat interlayer insulating film formed by acoating method.

In a light-emitting element, it is significant that the first electrodeis flat. If the flattening insulating film 1007 is not flat, there is arisk that the first electrode does not become flat due to the effect ofthe surface unevenness of the flattening insulating film 1007.Therefore, the flatness of the flattening insulating film 1007 issignificant.

Further, drain or source wirings 1024 a and 1024 b of a TFT have atwo-layer structure. In a portion to connect with the transparentconductive film later, the lower layer 1024 a of the drain or sourcewiring has a larger width than the upper layer 1024 b of the drain orsource wiring. This electrode shape is obtained by patterning twice toform the projected portion in accordance with Embodiment Mode 2. Here,the lower layer 1024 a of the drain or source wiring is formed with atitanium film and the upper layer 1024 b of the drain or source wiringis formed with an aluminum film. The upper layer 1024 b of the drain orsource wiring of the TFT is preferably tapered in consideration of thecoverage of the interlayer insulating film.

The side surface of the lower layer may have a smaller tapered anglethan the side surface of the upper layer in accordance with EmbodimentMode 1.

Further, a partition wall 1009 is formed with resin and serves as apartition between the layers containing the organic compound showingdifferent light emission. Therefore, the partition wall 1009 has agrating shape so as to surround one pixel, that is, a light-emittingregion. Although the layers containing the organic compound showing thedifferent light emission may overlap on the partition wall, the layersshould not overlap the first electrode of the adjacent pixel.

The light-emitting element includes a first electrode 1008 containing atransparent conductive material, layers 1015R, 1015G, and 1015B eachcontaining an organic compound, and a second electrode 1010. In thisembodiment, the first electrode 1008 is in contact with the lowerelectrode 1024 a so that they are electrically connected.

Further, the materials of the first electrode 1008 and the secondelectrode 1010 need to be selected in consideration of the workfunction. However, the first electrode and the second electrode can beeither an anode or a cathode. When the polarity of a driver TFT is ap-channel type, the first electrode is preferably an anode and thesecond electrode is preferably a cathode. Further, when the polarity ofa driver TFT is an n-channel type, the first electrode is preferably acathode and the second electrode is preferably an anode.

Moreover, the layers 1015R, 1015G, and 1015B containing the organiccompound are formed by stacking HIL (hole-injecting layer), HTL(hole-transporting layer), EML (light-emitting layer), ETL(electron-transporting layer), and EIL (electron-injecting layer) inorder from the side of the first electrode (anode). The layer containingthe organic compound can have, in addition to the multilayer structure,a single-layer structure or a mixed structure. To achieve full color,the layers 1015R, 1015G, and 1015B containing the organic compound areformed selectively to form three kinds of pixels of R, G, and B.

Further, it is preferable to provide protective films 1011 and 1012covering the second electrode 1010 in order to protect thelight-emitting element from any damages due to moisture or degas. As theprotective films 1011 and 1012, a dense inorganic insulating film (suchas a SiN film or a SiNO film) by a PCVD method, a dense inorganicinsulating film (such as a SiN film or a SiNO film) by a sputteringmethod, a thin film containing carbon as its main component (such as aDLC film, a CN film, or an amorphous carbon film), a metal oxide film(such as WO₂, CaF₂, or Al₂O₃), or the like is preferably used.

Space 1014 between the first substrate 1001 and a second substrate 1016are filled with a filling material or inert gas. In the case of fillinginert gas such as nitrogen, a dry agent for drying is preferablyprovided in the space 1014.

Moreover, light from the light-emitting element is extracted through thefirst substrate 1001. FIG. 9 shows a light-emitting device of abottom-emission type.

Although an example of a top-gate TFT is described in this embodiment,the present invention can be applied regardless of a TFT structure. Forexample, the present invention can be applied to a bottom-gate (invertedstaggered) TFT or a staggered TFT.

This embodiment can be freely combined with any one of Embodiment Modes1 to 3.

Embodiment 2

This embodiment describes an example of a light-emitting device in whichlight can be extracted from both substrates by forming a pixel portion,a driver circuit, and a terminal portion over the same substrate withreference to FIG. 10.

After forming a base insulating film over a substrate 610, eachsemiconductor layer is formed. Next, after forming a gate insulatingfilm covering the semiconductor layer, each gate electrode and terminalelectrode are formed. Subsequently, the semiconductor is doped with animpurity element imparting n-type conductivity (typified by phosphorusor arsenic) to form an n-channel TFT 636, and the semiconductor is dopedwith an impurity element imparting p-type conductivity (typified byboron) to form a p-channel TFT 637. Thus, a source region, a drainregion, and, if necessary, an LDD region are formed appropriately. Next,after forming a silicon nitride oxide film (SiNO film) containinghydrogen obtained by a PCVD method, activation of the impurity elementdoped in the semiconductor layer and hydrogenation are conducted.

Next, a flattening insulating film 616 to be an interlayer insulatingfilm is formed. As the flattening insulating film 616, an insulatingfilm whose skeletal structure includes a bond of silicon (Si) and oxygen(O) obtained by a coating method is used.

Next, a contact hole is formed in the flattening insulating film using amask and, at the same time, the flattening insulating film at aperiphery is removed.

Next, etching is conducted using the flattening insulating film 616 as amask to remove selectively an exposed part of the SiNO film containinghydrogen or the gate insulating film.

After forming a conductive film, etching is conducted using the mask,thereby forming a drain wiring and a source wiring. The drain wiring hasa two-layer structure, and the lower layer has a larger width than theupper layer in a portion to connect with the transparent conductive filmlater. In this embodiment, a portion where the lower layer is projectedfrom the upper layer is formed in accordance with the steps ofEmbodiment Mode 1. Further, the side surface of the lower layer has asmaller tapered angle than the side surface of the upper layer.

Next, a first electrode 623 including a transparent conductive film,that is, an anode (or a cathode) of the organic light-emitting elementis formed. The first electrode 623 is electrically connected to theprojected portion of the lower layer.

Next, an SOG film (for example, a SiO_(x) film containing an alkylgroup) obtained by a coating method is patterned, thereby forming aninsulator 629 (referred to as a bank, a partition wall, a barrier, anembankment, or the like) covering an end portion of the first electrode623.

Next, a layer 624 containing an organic compound is formed by anevaporation method or a coating method. Next, a second electrode 625including a transparent conductive film, that is, a cathode (or ananode) of the organic light-emitting element is formed. Next, atransparent protective layer 626 is formed by an evaporation method or asputtering method. The transparent conductive layer 626 protects thesecond electrode 625.

Next, the light-emitting element is sealed by pasting a transparentsealing substrate 633 with a sealing material 628. That is to say, thelight-emitting display device is sealed with a pair of substrates insuch a way that the circumference of the display region is surrounded bythe sealing material. Since the interlayer insulating film of the TFT isprovided over the whole surface of the substrate, there is a risk thatmoisture or impurities intrude through a part of the interlayerinsulating film located outside the pattern of the sealing material inthe case where the pattern of the sealing material is drawn more inwardthan the circumference of the interlayer insulating film. Therefore, thesealing material is provided so as to cover the end portion of theflattening insulating film by overlapping the inside of the pattern ofthe sealing material, preferably the pattern of the sealing material, atthe circumference of the flattening insulating film used as theinterlayer insulating film of the TFT. The region surrounded by thesealing material 628 is filled with a transparent filling material 627.

Finally, an FPC 632 is pasted to the terminal electrode by ananisotropic conductive film 631 according to a known method. Theterminal electrode is preferably formed with a transparent conductivefilm over the terminal electrode formed at the same time as the gatewiring (FIG. 10).

Further, light from the light-emitting element is extracted to bothsides through the substrate 610 and the sealing substrate 633. FIG. 10shows a light-emitting device having a structure in which light isextracted through both of the substrate and the sealing substrate.

According to the above steps, the pixel portion, the driver circuit, andthe terminal portion can be formed over the same substrate.

This embodiment can be freely combined with any one of Embodiment Modes1 to 3.

Embodiment 3

This embodiment describes an example of mounting a driver IC or an FPCin an EL display panel manufactured by the above embodiment.

FIG. 11A is a top view showing an example of a light-emitting device inwhich FPCs 1209 are pasted to four terminal portions 1208. Over asubstrate 1210, a pixel portion 1202 including a light-emitting elementand a TFT, a gate side driver circuit 1203 including a TFT, and a sourceside driver circuit 1201 including a TFT are formed. When achannel-forming region of the TFT is formed with a semiconductor filmhaving a crystal structure, these circuits can be formed over the samesubstrate. Therefore, an EL display panel in which a system-on-panel isachieved can be manufactured.

A part of the substrate 1210 except the contact portion is covered witha protective film, and a base layer containing a material having aphotocatalyst function is provided over the protective film.

Further, connection regions 1207 are provided at two locations so as tosandwich the pixel portion in order that the second electrode of thelight-emitting element contacts the wiring of the lower layer. The firstelectrode of the light-emitting element is electrically connected withthe TFT provided in the pixel portion.

A sealing substrate 1204 is fixed to the substrate 1210 by a sealingmaterial 1205 surrounding the pixel portion and the driver circuit and afilling material surrounded by the sealing material 1205. Further, afilling material containing a transparent dry agent may be used.Further, a dry agent may be disposed in a region not overlapping thepixel portion.

FIG. 11A shows a structure which is preferable for a light-emittingdevice having a relatively large size of an XGA class (for example, 4.3inch diagonal). Meanwhile, FIG. 11B shows an example of employing a COGmethod which is preferable for a small size (for example, 1.5 inchdiagonal).

In FIG. 11B, a driver IC 1301 is mounted onto a substrate 1310, and anFPC 1309 is mounted onto a terminal portion 1308 disposed at a tip ofthe driver IC. A plurality of the driver ICs 1310 to be mounted arepreferably formed over a rectangular substrate having a side of 300 mmto 1000 mm or more. That is to say, a plurality of circuit patternshaving a driver circuit portion and an input/output terminal as a unitmay be formed over the substrate, and each circuit pattern may be takenout by dividing the substrate at the last. The driver IC may have arectangular shape whose long side has a length of 15 to 80 mm and shortside has a length of 1 to 6 mm in consideration of the length of thepixel portion on a side or the pixel pitch. The length of the long sideof the driver IC may be equal to one side of the pixel region or a sumof the length of one side of the pixel portion and the length of oneside of the driver circuit.

The priority of the outside dimension of the driver IC to the IC chiplies in the length of the long side. When the driver IC has a long sideof 15 to 80 mm, the number required for mounting in accordance with thepixel portion is fewer than that in the case of using the IC chip,thereby increasing the yield of the production. When the driver IC isformed over a glass substrate, the shape of the substrate used as a basematerial is not limited and the productivity is not lowered. This is agreat advantage in comparison with the case of taking IC chips from acircular silicon wafer.

Further, a TAB method is also applicable. In a TAB method, a pluralityof tapes may be pasted and the driver IC may be mounted to the tapes.Similarly to the COG method, a single driver IC may be mounted to asingle tape. In such a case, a metal chip or the like for fixing thedriver IC is preferably pasted in point of the strength.

The substrate 1310 is covered with a protective film in a portion otherthan the contact portion. A base layer containing a material having aphotocatalyst function is provided over the protective film.

Further, a connection region 1307 is provided between the pixel portion1302 and the driver IC 1301 so that the second electrode of thelight-emitting element contacts the wiring of the lower layer. It is tobe noted that the first electrode of the light-emitting element iselectrically connected with the TFT provided in the pixel portion.

Further, the sealing substrate 1304 is fixed to the substrate 1310 by asealing material 1305 surrounding the pixel portion 1302 and a fillingmaterial surrounded by the sealing material.

When the channel-forming region of the TFT is formed with an amorphoussemiconductor film, the structure of FIG. 11B is employed even thoughthe size is large because the driver circuit is difficult to be formedover the same substrate.

This embodiment can be freely combined with any one of Embodiment Modes1 to 3 and Embodiments 1 and 2.

Embodiment 4

This embodiment shows an example of a liquid crystal display device inwhich a pixel portion, a driver circuit, and a terminal portion areformed over the same substrate with reference to FIG. 12. FIG. 12 is across-sectional view of a liquid crystal panel not using a color filter.

This embodiment employs a field sequential driving method in whichoptical shutter is conducted by a liquid crystal panel not using a colorfilter and a backlight of three colors of RGB is blinked at high speed.According to the field sequential method, color display is achieved bycontinuous time additive color mixing utilizing a temporal resolutionlimit of a human eye.

Three TFTs 703 are provided over a first substrate 701 where a baseinsulating film 702 is provided. These TFTs are n-channel TFTs eachhaving a channel-forming region 720, low-concentration impurity regions725 and 726, source or drain regions 721 and 722, a gate insulating film705, and a gate electrode. The gate electrode has two layers including atapered lower layer 723 a and an upper layer 723 b.

The interlayer insulating film 706 is an inorganic insulating film. Aflattening insulating film 707 covering the interlayer insulating film706 is a flat interlayer insulating film formed by a coating method.

The drain wiring or the source wiring of the TFT has a two-layerstructure. In a portion to connect with the transparent conductive filmlater, the lower layer 724 a of the drain or source wiring has a largerwidth than the upper layer 724 b of the drain or source wiring. Here,the lower layer of the drain or source wiring is formed with a Mo film,and the upper layer of the drain or source wiring is formed with analuminum film. The drain or source wiring of the TFT preferably has atapered shape in consideration of the coverage of the interlayerinsulating film.

The pixel electrode 708 can be formed with a transparent conductive filmsuch as ITO (indium tin oxide), ITSO (indium tin oxide containingsilicon oxide obtained by a sputtering method using a target of ITOwhich contains silicon oxide by 2 to 10 wt %), a light-transmittingconductive oxide film (IZO) in which zinc oxide (ZnO) is mixed intoindium oxide containing silicon oxide by 2 to 20%, or ATO (antimony tinoxide) containing silicon oxide.

A pillar spacer 714 contains resin and serves to keep the distancebetween the substrates constant. Therefore, the pillar spacers 714 areprovided at uniform intervals. For higher speed response, the distancebetween the substrates is preferably 2 μm or less and the height of thepillar spacer 714 is appropriately adjusted. When the screen size is assmall as 2 inch or less on a side, the pillar spacers are notnecessarily provided. The distance between the substrates may beappropriately adjusted only with a gap material such as a filler to bemixed into the sealing material.

Further, an orientation film 710 for covering the pillar spacer 714 andthe pixel electrode 708 is provided. An orientation film 712 is alsoprovided to the second substrate 716 to be an opposing substrate, andthe first substrate 701 and the second substrate 716 are pasted with asealing material (not shown).

The space between the first substrate 701 and the second substrate 716is filled with a liquid crystal material 711. The substrates may bepasted to each other by dropping the liquid crystal material 711 underlow pressure so that a bubble does not enter by the sealing materialhaving a closed pattern. Alternatively, a dip method (pumping method)may be employed in which the liquid crystal is injected using capillaryphenomenon after providing a seal pattern having an opening portion andpasting the TFT substrate.

A liquid crystal panel in this embodiment has a so-called π cellstructure which uses an OCB (optically compensated bend) display mode.The π cell structure is a structure in which liquid crystal moleculesare orientated in such a way that the pretilt angles of the liquidcrystal molecules are in a plane-symmetric relation to a center planebetween the active matrix substrate and the opposing substrate. Theorientation state of the π cell structure is splay orientation whenvoltage is not applied to the substrates, and shifts to bend orientationwhen voltage is applied. When the voltage is further applied, the liquidcrystal molecules of the bend orientation are orientated perpendicularto the both substrates so that light can pass therethrough. In the OCBmode, response speed gets about 10 times higher than in a conventionalTN mode.

Further, the liquid crystal panel is sandwiched between a pair ofoptical films (a polarizing plate, a retarder, or the like) 731 and 732.In addition, in the display using the OCB mode, a biaxial retarder ispreferably used to compensate the viewing angle dependence of theretardation three-dimensionally.

An LED 735 of three colors of RGB is used as a backlight for a liquidcrystal panel shown in FIG. 12. Light from the LED 735 is led by alight-guide plate 734. In the field sequential driving method, the LEDis turned on in order of R, G, and B in a TR period, a TG period, and aTB period of an LED lighting period. In a lighting period (TR) of a redLED, a video signal (R1) corresponding to red is supplied to a liquidcrystal panel, and a red image for one screen is written in the liquidcrystal panel. In a lighting period (TG) of a green LED, video data (G1)corresponding to green is supplied to the liquid crystal panel and agreen image for one screen is written in the liquid crystal panel. In alighting period (TB) of a blue LED, video data (B1) corresponding toblue is supplied to the liquid crystal display device, and a blue imagefor one screen is written in the liquid crystal panel. One frame isformed by writing these three images.

Embodiment 5

Various electronic appliances can be manufactured by incorporating an ELpanel or a liquid crystal panel obtained by the present invention. Theelectronic appliance is, for example, a camera such as a video camera ora digital camera, a goggle-type display, a navigation system, a soundreproduction apparatus (a car audio, an audio component, and so on), apersonal computer, a game machine, a mobile information terminal (amobile computer, a mobile phone, a mobile game machine, an electronicbook, and so on), an image reproduction device equipped with a recordingmedium (specifically, a device which can reproduce a recording mediumsuch as a digital versatile disk (DVD) and has a display for showing theimage), and so on. FIGS. 13A to 13H and FIG. 14 show specific examplesof these electronic appliances.

FIG. 13A shows a television including a case 2001, a supporting stand2002, a display portion 2003, speaker portions 2004, a video inputterminal 2005, and the like. The present invention is applied tosemiconductor integrated circuits built in the television and thedisplay portion 2003, and thus, the television consuming less electricpower can be achieved. It is to be noted that all the televisions for apersonal computer, TV broadcasting reception, advertisement display, andso on are included.

FIG. 13B shows a digital camera including a main body 2101, a displayportion 2102, an image receiving portion 2103, operation keys 2104, anexternal connection port 2105, a shutter 2106, and so on. The presentinvention is applied to semiconductor integrated circuits (a memory, aCPU, and the like) built in the digital camera and thus, the digitalcamera consuming less electric power can be provided.

FIG. 13C shows a personal computer including a main body 2201, a case2202, a display portion 2203, a keyboard 2204, an external connectionport 2205, a pointing mouse 2206, and the like. The present invention isapplied to semiconductor integrated circuits (such as a memory or a CPU)built in the personal computer and the display portion 2203. Thus, thecontact resistance and the wirings used in TFTs provided in the displayportion and a CMOS circuit constituting a part of a CPU can be decreasedand the personal computer consuming less electric power can be achieved.

FIG. 13D shows an electronic book including a main body 2301, a displayportion 2302, a switch 2303, operation keys 2304, an infrared port 2305,and the like. The present invention can be applied to semiconductorintegrated circuits (such as a memory or a CPU) built in an electronicbook and the display portion 2302, and the electronic book consumingless electric power can be achieved.

FIG. 13E shows a mobile image reproduction device equipped with arecording medium (specifically a DVD reproduction device), including amain body 2401, a case 2402, a display portion A2403, a display portionB2404, a recording medium (such as a DVD) reading portion 2405,operation keys 2406, speaker portions 2407, and so on. The displayportion A2403 mainly displays image information, and the display portionB2404 mainly displays text information. The present invention is appliedto semiconductor integrated circuits (such as a memory or a CPU) builtin the image reproduction device and the display portions A2403 andB2404, and thus the image reproduction device consuming less electricpower can be achieved.

FIG. 13F shows a mobile game machine including a main body 2501, adisplay portion 2505, operation switches 2504, and so on. The presentinvention is applied to semiconductor integrated circuits (such as amemory or a CPU) built in the game machine and the display portion 2505,and thus, the game machine consuming less electric power can beachieved.

FIG. 13G shows a video camera including a main body 2601, a displayportion 2602, a case 2603, an external connection port 2604, a remotecontrol receiving portion 2605, an image receiving portion 2606, abattery 2607, an audio input portion 2608, operation keys 2609, and thelike. The present invention can be applied to semiconductor integratedcircuits (such as a memory or a CPU) built in the video camera and thedisplay portion 2602, and thus, the video camera consuming less electricpower can be achieved.

FIG. 13H shows a mobile phone including a main body 2701, a case 2702,an audio input portion 2704, an audio output portion 2705, operationkeys 2706, an external connection port 2707, an antenna 2708, and thelike. The present invention can be applied to semiconductor integratedcircuits (such as a memory, a CPU, or a high-frequency circuit) built inthe mobile phone and the display portion 2703, and thus, the mobilephone consuming less electric power can be achieved.

FIG. 14 shows a mobile music reproduction device equipped with arecording medium, including a main body 2901, a display portion 2903, arecording medium (a card type memory, a compact HDD, or the like)reading portion 2902, operation keys 2902 and 2906, speaker portions2905 of a headphone connected to a connection cord 2904, and the like.The present invention can be applied to the display portion 2903 and themusic reproduction device consuming less electric power can be achieved.

This embodiment can be freely combined with any one of Embodiment Modes1 to 3 and Embodiments 1 to 4.

What is claimed is:
 1. A semiconductor device comprising: asemiconductor layer over a substrate; a source electrode and a drainelectrode over and electrically connected to the semiconductor layer; afirst insulating layer over the source electrode and the drainelectrode; and a pixel electrode electrically connected to the sourceelectrode and the drain electrode, wherein one of the source electrodeand the drain electrode comprises a first electrode layer and a secondelectrode layer on the first electrode layer, wherein the firstelectrode layer comprises titanium, wherein the second electrode layercomprises aluminum, wherein a first width of the first electrode layeris larger than a second width of the second electrode layer, wherein anupper surface of the second electrode layer is in contact with the firstinsulating layer, wherein the first electrode layer is in contact withthe pixel electrode, wherein the semiconductor layer comprises anamorphous silicon, and wherein the pixel electrode comprises an ITO. 2.The semiconductor device according to claim 1, wherein the secondelectrode layer is in contact with the pixel electrode.
 3. Thesemiconductor device according to claim 1, further comprising a secondinsulating layer between the semiconductor layer and the one of thesource electrode and the drain electrode.
 4. The semiconductor deviceaccording to claim 1, further comprising a gate electrode adjacent tothe semiconductor layer, wherein the gate electrode comprises tantalumnitride and tungsten.
 5. The semiconductor device according to claim 1,further comprising an orientation film over the pixel electrode and aliquid crystal layer over the orientation film.
 6. The semiconductordevice according to claim 1, further comprising a gate electrodeadjacent to the semiconductor layer, wherein the gate electrode, thesemiconductor layer, the source electrode, and the drain electrode areprovided in a pixel region.
 7. A semiconductor device comprising: asemiconductor layer over a substrate; an electrode or a wiring over andelectrically connected to the semiconductor layer; a first insulatinglayer over the electrode or the wiring; and a pixel electrodeelectrically connected to the electrode or the wiring, wherein theelectrode or the wiring comprises a first conductive layer and a secondconductive layer on the first conductive layer, wherein the firstconductive layer comprises titanium, wherein the second conductive layercomprises a low-resistant metal, wherein a first width of the firstconductive layer is larger than a second width of the second conductivelayer, wherein an upper surface of the second conductive layer is incontact with the first insulating layer, wherein the first conductivelayer has a portion extending from an end portion of the secondconductive layer, wherein at least a part of the extending portion ofthe first conductive layer is in contact with the pixel electrode,wherein the semiconductor layer comprises an amorphous silicon, andwherein the pixel electrode comprises an ITO.
 8. The semiconductordevice according to claim 7, wherein the second conductive layer is incontact with the pixel electrode.
 9. The semiconductor device accordingto claim 7, further comprising a second insulating layer between thesemiconductor layer and the electrode or the wiring.
 10. Thesemiconductor device according to claim 7, further comprising a gateelectrode adjacent to the semiconductor layer, wherein the gateelectrode comprises tantalum nitride and tungsten.
 11. The semiconductordevice according to claim 7, wherein the low-resistant metal comprisesaluminum.
 12. The semiconductor device according to claim 7, furthercomprising an orientation film over the pixel electrode and a liquidcrystal layer over the orientation film.
 13. The semiconductor deviceaccording to claim 7, further comprising a gate electrode adjacent tothe semiconductor layer, wherein the gate electrode, the semiconductorlayer, and the electrode or the wiring are provided in a pixel region.14. The semiconductor device according to claim 7, wherein the firstconductive layer has a first tapered angle and the second conductivelayer has a second tapered angle, and wherein the first tapered angle isdifferent from the second tapered angle.
 15. The semiconductor deviceaccording to claim 7, wherein the second conductive layer is not incontact with the pixel electrode.
 16. A semiconductor device comprising:a semiconductor layer over a substrate; a first conductive layercomprising titanium, the first conductive layer being in contact withthe semiconductor layer; a second conductive layer on the firstconductive layer; a first insulating layer over the second conductivelayer; and a third conductive layer comprising an ITO over the secondconductive layer, the third conductive layer being in contact with anend portion and a part of a top surface of the second conductive layer,wherein the third conductive layer is in contact with the firstconductive layer, wherein a first width of the first conductive layer islarger than a second width of the top surface of the second conductivelayer, wherein the second conductive layer comprises a low-resistantmetal, wherein the semiconductor layer comprises an amorphous silicon,and wherein an extending portion of the third conductive layer is apixel electrode, and wherein the pixel electrode is provided over thefirst insulating layer.
 17. The semiconductor device according to claim16, further comprising a gate electrode adjacent to the semiconductorlayer, wherein the gate electrode comprises tantalum nitride andtungsten.
 18. The semiconductor device according to claim 16, whereinthe low-resistant metal comprises aluminum.
 19. The semiconductor deviceaccording to claim 16, wherein the first conductive layer and the secondconductive layer form a source electrode and a drain electrode.
 20. Asemiconductor device comprising: a semiconductor layer over a substrate;a source electrode and a drain electrode over and electrically connectedto the semiconductor layer; a first insulating layer over the sourceelectrode and the drain electrode; and a pixel electrode electricallyconnected to the source electrode and the drain electrode, wherein oneof the source electrode and the drain electrode comprises a firstconductive layer and a second conductive layer on the first conductivelayer, wherein the first conductive layer comprises titanium, whereinthe second conductive layer comprises aluminum, wherein a first width ofthe first conductive layer is larger than a second width of the secondconductive layer, wherein an upper surface of the second conductivelayer is in contact with the first insulating layer, wherein the firstconductive layer has a portion extending from an end portion of thesecond conductive layer, and wherein at least a part of the extendingportion of the first conductive layer is in contact with the pixelelectrode.
 21. The semiconductor device according to claim 20, furthercomprising a gate electrode adjacent to the semiconductor layer.
 22. Thesemiconductor device according to claim 20, further comprising a lightemitting layer over the pixel electrode.